In this testing ground, do you think someone playing a 3 button tracer spammer will do above average against a bunch of melee who dont have much situational awareness? Cause i do, i really think they sit their and go "Oh look at mister XXX going all crazy mando on the rest of us, clearly peoples whining is not justified..the class is just too hard to master."
Your point is a major factor in why Merc dps is considered OP by the devs. Not so much the issue of what happens when devs play devs in their free time. But just generally, a low skill Merc dps will own a low skill Melee dps. The low skill melee dps can't keep his target in front of him and in range. He might lose 50% or more of his GCDs simply to target acquisition. The low skill Merc dps has a significantly easier time here. And thus he will post better numbers in warzones. But once you get to skilled players, that melee inefficiency is dramatically reduced. Instead you get a lot of lost GCDs to the Merc dps through interrupts and lost dps through better defensive abilities available to the melee.
Basically, the Merc dps subclass benefits from a very easy learning curve and is thus penalized by the devs with an artificially low ceiling on performance. It's bad design.